1. Field of the Invention
The invention relates to triarylamine based trimer monomers and to low band gap polymers and copolymers prepared therefrom and in particular to optoelectronic devices such as electroluminescent devices and photovoltaic devices comprising such polymers and copolymers.
2. Description of Related Technology
Semiconductive organic polymers have been known for several decades, during the past ten years they have seen increasing application in the field of electroluminescent devices, see for example WO90/13148. A typical electroluminescent device comprises an anode, a cathode and a layer of light-emitting material situated between the anode and the cathode, further layers may also be introduced to improve charge injection into the device or charge transport through the device. Semiconductive organic polymers may act as the light-emitting component or as charge transport or charge injecting components in electroluminescent devices. More recently semiconductive organic polymers have found application in photovoltaic devices, as disclosed in WO96/16449, and also as photoconductors and photodetectors.
The nature of the polymeric material used in electroluminescent devices is critical to the performance of the device, materials used include poly(phenylenevinylenes), as disclosed in WO90/13148, polyfluorenes, as disclosed in WO97/05184, poly(arylamines), as disclosed in WO98/06773. In particular copolymers and blends of polymers have been found to be useful in such devices, as disclosed in WO92/03490, WO99/54385, WO00/55927 and WO99/48160. Poly(arylamines) have been disclosed in which the aromatic groups may comprise heteroaromatic moieties such as triazine, see WO01/49769.
Recently there have been efforts to increase the range of available semiconductive polymers and, in particular, to provide polymers with lower band gaps, see WO01/49768. The band gap is the difference in energy levels between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Low band gap materials emit light at longer wavelengths i.e. towards the red end of the visible region of the electromagnetic spectrum and are also promising candidates for polymeric photovoltaic devices. WO01/49768 discloses a range of low band gap polymers comprising heterocyclic moieties such as benzothiadiazole. Benzothiadiazole is a functional group characterised by its light-emitting and electron transporting properties.